[time-nuts] World's most precise.... wall clock

[Attila Kinali]

On Tue, 02 Mar 2021 22:42:45 -0800
Hal Murray <hmurray at megapathdsl.net> wrote:

> The basic idea is to mount a magnet on a stiff wire so that it sticks out to 
> the side of the pendulum arm, then mount a coil so the magnet will swing 
> through it.  Now pulse the coil to get the desired results.

This is basically injection locking of a pendulum clock.
Pendulum clocks are very nice for injection locking, due
to their relatively low Q and because a magnetic field can
be easily adjusted in strength.

You don't need to place the magnet at any one specific position.
It is enough that it is somewhere in the path of the pendulum.
My favorite position is right beneath the center.

The injected pulses should be long enough to have an effect
with a reasonably weak magnetic field, but short enough to
be an impulse, from the point of view of the mechanical system.
I.e. the pulse length should be a fraction of the time it take
for the pendulum to pass the magnet. Somewhere between 1/2
and 1/10 should work in most cases.

Start with getting the pendulum clock as close to the right
rate as possible. Place the magnet where it suits you best.
Then adjust the current through the magnet such that you can
barely feel some resistance when you move the pendulum through
the field with your hands. Set your electronics to inject pulses
at the appropriate rate. This does not have to be at every pass,
but can be, e.g., every 10th pass. Now let the clock run and see
whether you get proper synchronization/locking. If not, increase
the current through the magnet step wise until it is strong enough
for synchronization. Test over varying temperatures, air humidity
and pressure to ensure that changes of the natural frequency of
the pendulum don't get your clock unlocked.

If you have trouble with keeping the clock locked and don't want
to increase the current any further, increase the pulse length.

For additionaly time-nuttyness, you can add a sensor somewhere in
the path of the pendulum and measure its phase versus true
time. Suitable sensors are fork light barriers and Hal sensors.


			Attila Kinal
-- 
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always 
wonder about. And that's why we do research.
		-- Kobayashi Makoto